This invention relates to a system for controlling the air intake of an engine, or more in particular to a system for controlling the idling speed of engine revolutions and the pressure in its air intake tube at the time of deceleration for a spark-ignition type of engine.
Generally, in the idling operation of a spark-ignition type of engine that is cold, viscosity of the lubricant is high and therefore friction loss is large. Thus more air than when the engine is warm is supplied to the engine to enable the engine to run against the friction and preferably the number of revolutions or engine speed is maintained high in order to shorten the warm-up period.
In a known system to achieve this purpose, an air duct tube bypassing the throttle valve is provided with a bi-metal air control valve midway thereof. In accordance with the engine temperature, the amount of air flowing through the duct tube is controlled, thus controlling the engine speed.
If the pressure in the air intake tube is reduced at the time of deceleration, pressure at the time of ignition in the engine combustion chamber is reduced, with the result that the fuel is fired erroneously, thereby discharging a great amount of harmful HC gases into the atmosphere. In the case where the exhaust system includes a catalyst reactor as an exhaust gas purifier, a great amount of HC reacts in the catalyst reactor, and the resulting heat of reaction overheats the catalyst reactor, often causing it to melt.
According to a known method for obviating such a problem, a special device having a diaphragm valve is mounted by which when the pressure in the air intake tube is reduced below a predetermined level, additional air is supplied into the engine, thus preventing the pressure in the air intake tube from decreasing below the setting.
In the above-mentioned engine speed control system, only the engine temperature is used as a control parameter. Therefore, the disadvantage is that when different types of engine lubricant are involved, the difference in lubricant viscosity makes it impossible to attain a high design speed or results in an engine speed higher than the design speed.
Another disadvantage of the above-mentioned conventional system is that since the engine speed control system and the air intake tube pressure control device for deceleration are mounted separately from each other, a larger mounting space is required. This necessitates the use of more air duct tubes and increases the cost of the system.